I needed a cage for my pet rats, so I decided to repurpose an old TV stand, that I found at a flea market for $5. A cage like this could be made from a number of types of furniture, for almost any type of small animal.
Step 1: Materials
As mentioned, the TV stand came from a flea market. I also got a 1x2 (82 cents), some wire, (about $5) and some spray paint. I already had, but one might need to buy, some small hinges, and a latch with a spring.